How to wire cpc in class rooms

[Darkwood]

What you are permitted to do is this.

CPC 1 from circuit 1 in terminal 1 along with CPC 1 from circuit 2
CPC 2 from circuit 1 in terminal 2 along with CPC 2 from circuit 2 etc etc.
Using this method takes up no extra ways on terminal block. This is only acceptable if the CPC's are all marked with their correct circuit number and the cu is labeled accordingly.

Ive honestly never heard this method may i ask where you got this from, although i understand it and how it avoids lost earth but see that it contravenes other regulations concerning termination position and seperation of terminated circuits, ive always had to add an additional earth bar for these purposes with the Niceic man saying this is the only acceptable way.... please enlighten me im interested where this method comes from.

 

[andyb]

Ive honestly never heard this method may i ask where you got this from, although i understand it and how it avoids lost earth but see that it contravenes other regulations concerning termination position and seperation of terminated circuits, ive always had to add an additional earth bar for these purposes with the Niceic man saying this is the only acceptable way.... please enlighten me im interested where this method comes from.

It's all down to interpretation of the regs, the niceic inspector told me this method & so it's the method I use.
Obviously the cpcs & the board need clear labeling but it makes sense to me.

 

[Sintra]

Ive honestly never heard this method may i ask where you got this from, although i understand it and how it avoids lost earth but see that it contravenes other regulations concerning termination position and seperation of terminated circuits, ive always had to add an additional earth bar for these purposes with the Niceic man saying this is the only acceptable way.... please enlighten me im interested where this method comes from.

Ok it complies with reg 543.7.1.4 & reg 543.7.1.5 regarding seperate terminations of the cpc and labelling.

Reg 514.1.2 States "As far as is reasonably practicle wiring shall be so arranged or marked that it can be identified for inspection, testing, repair or alteration of the installation"

So if the method i use is labelled correctly it also complies to the above reg.

I in the past have also used an additiional bar and would be my prefered method but on occasions have used the alternative one bar method.

NICEIC inspector disputed the one bar method on an assessment a few years back and when i pointed out that it complied to the regs he agreed.

 

[Darkwood]

Well it sounds like its tried and tested, but would enquire how you would mark this up then if for arguments sake rings are in circuit 4 and 5 then earth for circuit 4 will be tagged with 4's and circuit 5 with 5's respectively, now the earth bar is fixed with markings 1 to ......whatever, if you put earths 4 and 5 in terminal 4; earths 5 and 4 in terminal 5 then you have in my mind clearly made a termination that is in itself confusing to anyone following you, having an earth no'5 in terminal 4 is where i think it dosnt comply as you have a conflict of markings, please give me your thoughts as i do understand the reg's can sometimes be interpreted in different ways.
I totally understand that the board will be marked with label for high current earth etc but im asking around and no-one in my circle of sparkies has heard this so surely if its a little known method its likely to confuse others and ive yet to see this method in any onsite guides in picture form at least but maybe this is where i eat humble pie and you direct me to the guide and page.
Please dont get me wrong im not trying to prove you wrong im trying to understand where this method comes from as i dont like doing anything im not 100% certain about as i like to be as good as i can be i dont do things because im allowed to do thing i do things because i understand why i do them.

 

[andyb]

It probably isn't in any guide Darkwood, it's just a method of complying if there is no extra earth bar in the board.
As for identification, I use those little numbered rings that you can buy from the wholesaler & slip them over the earth sleeving.

 

[Darkwood]

It probably isn't in any guide Darkwood, it's just a method of complying if there is no extra earth bar in the board.
As for identification, I use those little numbered rings that you can buy from the wholesaler & slip them over the earth sleeving.

I too use the number rings but the point i was putting across if you re-read my last post was you will have an earth from each ring marked up and in confliction to the earth terminal it is in this invitably will lead to confusion for even a competent electrician following as this method isnt widely practiced to my knowledge, this in itself i feel dosn't meet with the reg's although it will meet reg's regarding earth seperation for the high earth current circuits.

 

[jimes]

doesnt the cpc have to be bigger with high earth leak equipment? cant remeber exact numbers.....

 

[Sintra]

No 1.5mm as in a T&E is fine in a ring.

 

[Sintra]

Well it sounds like its tried and tested, but would enquire how you would mark this up then if for arguments sake rings are in circuit 4 and 5 then earth for circuit 4 will be tagged with 4's and circuit 5 with 5's respectively, now the earth bar is fixed with markings 1 to ......whatever, if you put earths 4 and 5 in terminal 4; earths 5 and 4 in terminal 5 then you have in my mind clearly made a termination that is in itself confusing to anyone following you, having an earth no'5 in terminal 4 is where i think it dosnt comply as you have a conflict of markings, please give me your thoughts as i do understand the reg's can sometimes be interpreted in different ways.
I totally understand that the board will be marked with label for high current earth etc but im asking around and no-one in my circle of sparkies has heard this so surely if its a little known method its likely to confuse others and ive yet to see this method in any onsite guides in picture form at least but maybe this is where i eat humble pie and you direct me to the guide and page.
Please dont get me wrong im not trying to prove you wrong im trying to understand where this method comes from as i dont like doing anything im not 100% certain about as i like to be as good as i can be i dont do things because im allowed to do thing i do things because i understand why i do them.

Have a look at this guide from the iet.

View attachment High Integrity Earthing.PDF

 

[Darkwood]

Have a look at this guide from the iet.

View attachment 2491

Thx for the info' Sintra this is what i couldnt find myself but having read it im happy the method is acceptable and if i employ this method at least im now confident in its use, but reading the pdf you linked it does state that large dist' boards may come with many spare terminals, where some manufacturers may supply an accessory kit to add extra way, [where this is NOT an option, the following solution is one method].......thus the earth cross-over method is explained.
My interpretation of this is that an accessory kit needs to be fitted if you are short of spare earth terminations and only when this is not an option that it is one method to get around this problem, so i can see it been used in older dist' boards when installing new high earth circuits and spare ways or accessory kits are not available but if the board is been changed i would think a suitable board should be chosen and not relying on this method as routine.
Appreciate the feed back thanks..

 

[Darkwood]

doesnt the cpc have to be bigger with high earth leak equipment? cant remeber exact numbers.....

Its dependent on the expected mA leakage to earth if you look at the pdf Sintra sent me further down it explains when larger earth may be needed, this is also why you need to limit the number of sockets on a computer ring main:-
1. so you dont exceed the mA permitted for the smaller cpc arrangement.
2. rcd coverage would also become prone to tripping if too many computer points were wired on one ring.

 

[Sintra]

Thx for the info' Sintra this is what i couldnt find myself but having read it im happy the method is acceptable and if i employ this method at least im now confident in its use, but reading the pdf you linked it does state that large dist' boards may come with many spare terminals, where some manufacturers may supply an accessory kit to add extra way, [where this is NOT an option, the following solution is one method].......thus the earth cross-over method is explained.
My interpretation of this is that an accessory kit needs to be fitted if you are short of spare earth terminations and only when this is not an option that it is one method to get around this problem, so i can see it been used in older dist' boards when installing new high earth circuits and spare ways or accessory kits are not available but if the board is been changed i would think a suitable board should be chosen and not relying on this method as routine.
Appreciate the feed back thanks..

Agree 100% i have only used the method in an insulated cu where there is no possibility of an additional bar etc.